Understanding the impact of natural atmospheric particles

An international team of scientists, led by the University of Leeds, has quantified the relationship between natural sources of particles in the atmosphere and climate change.

Their study, published today in Nature Geoscience, shows that the
cooling effect of natural atmospheric particles is greater during warmer years
and could therefore slightly reduce the amount that temperatures rise as a
result of climate change.

Particles in the atmosphere can alter Earths climate by absorbing
or reflecting sunlight. These particles are often produced by human activities,
such as from cars and industry, but there are also naturally occurring
particles.

The team combined atmospheric measurements with a computer model
to map the effects of two natural particle sources: smoke from forest fires and
the gases emitted by trees that can stick together to form tiny particles.

Study lead author Dr Catherine Scott, from the School of Earth and Environment at Leeds,
said: Natural particles can alter the climate, but they are also strongly
controlled by it.

As the Earth warms, plants release more volatile gases from
their leaves - these are the gases that, for example, give pine forests a piney
smell. Once in the air these gases can form tiny particles. More particles in
the atmosphere reflect away the Suns energy, which helps to cool the planet.

This cooling offsets some of the temperature rise and is known
as a negative climate feedback. We can think of forests acting as giant air
conditioners slightly reducing the warming due to greenhouse gas emissions.

Study co-author Dominick Spracklen, Professor of
Biosphere-Atmosphere Interactions at Leeds, said: Overall the response of the
climate to an initial warming is to amplify that warming, ie a positive
feedback.

This natural negative feedback might act to offset a small
amount of warming due to climate change but it is not enough to counteract
other strong positive feedbacks in the climate system. This means reductions in
greenhouse gas emissions are still required to prevent dangerous levels of
global warming.

Our research highlights the need for these complex interactions
to be well represented in climate models. The latest generation of models being
used for future climate projections include more detail about the way that the
atmosphere and the land surface interact than ever before  but its important
that we can isolate the role that these processes are playing as the climate
evolves.

Further information

The
research paper, Substantial large-scale
feedbacks between natural aerosols and climate, is published in Nature Geoscience on 4 December 2017.

For
additional information and to request interviews please contact Anna Harrison,
Press Officer at the University of Leeds, on +44 (0)113 34 34196 or a.harrison@leeds.ac.uk